The first mechanical alarm clock could only ring at 4:00 AM.

Before mechanical alarms, people used the sun, animals, or paid 'knocker-ups' who tapped on windows with sticks to wake them. Levi Hutchins was a clockmaker from New Hampshire who wanted a reliable way to start his day at 4:00 AM. He built a wooden cabinet with a brass clock inside that had one extra gear. This gear was set to trip a lever that struck a bell only when the clock reached that hour.The alarm was part of the clock's inner machinery. There were no buttons or dials to move the alarm time to a different hour. Hutchins did not patent his invention because he only made it for himself. He believed 4:00 AM was the best time to start a productive day. It took another 60 years for someone to invent an alarm you could change.In 1847, a French clockmaker named Antoine Redier patented the first adjustable alarm clock. This version used a movable dial so people could choose their own wake-up time. Later, in 1876, Seth E. Thomas patented a version in the United States that was easier to mass-produce. This allowed alarm clocks to become common in homes everywhere. Modern digital clocks now use electronic oscillators to keep time and can be set to any second of the day.